The present invention relates to an optical lens provided on an optical information recording and reproducing apparatus capable of conducting at least one of recording of information on an optical recording medium and reproducing of information recorded on an optical recording medium, and to an optical information recording and reproducing apparatus equipped with the optical lens mentioned above.
There has been known an optical pickup apparatus (optical information recording and reproducing apparatus) that conducts recording of information on an optical recording medium and reproducing of information recorded on an optical recording medium. In the optical pickup apparatus, a ray of light emitted from a semiconductor laser light source is converged on an information recording surface of an optical recording medium by an objective lens so that information may be recorded or reproduced.
In an objective lens of the optical pickup apparatus, there is provided an antireflection coating on the surface for improving efficiency of using light. Coating of the antireflection coating is conducted by, for example, a vacuum deposition method or a sputtering method. It has been common to form antireflection coating 11 so that its thickness may vary to be thinner as a position of that thickness is farther from center portion C toward peripheral portion P of objective lens 10, as shown in FIG. 8.
Further, thickness of the antireflection coating 11 at the center portion C is established so that reflectance on the center portion C of the objective lens 10 for light entering at an incident angle of 90xc2x0 may show the minimum value. Namely, the thickness of the antireflection coating 11 is established so that an amount of light passing through the center portion C of the objective lens 10 may be the largest.
Incidentally, it is generally known that the thinner an antireflection coating is in thickness, the more a wavelength-dependence of reflectance for light is shifted to the shorter wave side. Further, in the antireflection coating, it is known that the greater an incident angle of light is, the more a wavelength-dependence of reflectance for light is shifted to the shorter wave side.
In the conventional objective lens 10, as stated above, antireflection coating 11 is thinner in thickness when a position of that thickness is farther from center portion C toward peripheral portion P of objective lens 10, and an incident angle of light is greater when a position of the incidence is farther from center portion C toward peripheral portion P.
In the conventional objective lens 10, therefore, the wavelength-dependence of reflectance for light on the peripheral portion P has been shifted more to the shorter wavelength side than that on the center portion C. Therefore, the wavelength for which the reflectance for light entering at the peripheral portion P shows the minimum value has been shorter than the wavelength for which the reflectance for light entering at the center portion C shows the minimum value.
Accordingly, in the aforementioned conventional objective lens 10, reflectance of peripheral portion P for a laser beam is higher, although that of central portion C for the laser beam is low, and therefore, an amount of light passing through the peripheral portion P has been less relatively, compared with an amount of light passing through the central portion C. Accordingly, there have been problems such as an increase of a beam spot diameter caused by a decline of converging power for light and a fall of an amount of light of a beam.
To solve these problems, it can be considered that the antireflection coating 11 on the peripheral portion P is made to be thick so that an amount of light passing through the peripheral portion P may be large. However, in this case, thickness of antireflection coating 11 on the center portion C is also increased together with an increase in thickness of the antireflection coating 11 on the peripheral portion P. Therefore, wavelength-dependency of reflectance on the center portion C for light entering at an incident angle of 90xc2x0 is more shifted to the long wavelength side, and a wavelength becomes longer than that wherein reflectance shows the minimum value, which lowers an amount of light passing through the center portion C.
Namely, in the conventional objective lens 10, it was impossible to make reflectance on peripheral portion P for light entering obliquely to be small and to make reflectance on center portion C for light entering vertically to be small, at the same time, which has made it difficult to make both light-converging power and an amount of light to be optimum.
In recent years, it has been tried to make a diameter of an optical beam spot small, for a larger capacity of an optical recording medium, and as an example for that, a technology of a higher NA (Numerical Aperture) of an objective lens has been advanced. However, curvature of the lens surface of an objective lens having high NA is great, and therefore, an incident angle for light on the peripheral portion P of the lens is extremely large, and it is a remarkable tendency that thickness of the antireflection coating 11 on the peripheral portion P becomes smaller.
Due to this, an amount of light passing through the peripheral portion P is lowered extremely, and an increase of a spot diameter cannot be controlled despite an objective lens having high NA, resulting in an increase of cross talk and in deterioration of jitter characteristics, which has interfered with a large capacity of an optical recording medium.
With a background of the problems stated above, an object of the invention is to provide an optical lens wherein a spot diameter can be made small and an amount of light passing the optical lens can be secured, and an optical information recording and reproducing apparatus equipped with the optical lens.
In particular, the object of the invention is to provide an optical lens having an excellent light-converging characteristic and high NA, and to provide an optical information recording and reproducing apparatus wherein a large capacity of an optical recording medium can be realized.
To solve the problems mentioned above, Structure (1) of the invention is an optical lens that is provided on an optical information recording and reproducing apparatus capable of conducting at least one of recording information on an optical recording medium and reproducing of information recorded on an optical recording medium, by converging light on the optical recording medium, wherein an antireflection coating is provided on the lens surface on at least one side thereof, and the thickness of the antireflection coating on the peripheral portion of the lens surface is greater than that of the antireflection coating provided on the center portion of the lens surface.
In the invention described in Structure (1), it is possible to control so that wavelength-dependency of reflectance on the peripheral portion of the lens surface for light may be shifted less to the short wavelength side for wavelength-dependency of reflectance on the center portion of the lens surface, compared with the convention objective lens, because the thickness of the antireflection coating on the peripheral portion of the lens surface is greater than that of the antireflection coating provided on the center portion of the lens surface.
It is therefore possible to control so that reflectance of the peripheral portion of the lens surface for light may not become high even when thickness of the antireflection coating on the center portion is set so that reflectance on the center portion of the lens surface may be low, which is different from the conventional objective lens. It is therefore possible to prevent a fall of an amount of light passing through the peripheral portion of the lens, and to improve a light-converging power to make a spot diameter small and to secure an amount of light passing through the lens, compared with the past.
Structure (2) of the invention is the optical lens according to Structure (1), wherein when an angle formed by a normal line at a certain position on the lens surface where the antireflection coating is provided and by an optical axis is represented by xcex8, thickness of the antireflection coating on the peripheral portion of the lens surface on which the angle xcex8 is 45xc2x0 or more is greater than that on the center portion of the lens surface on which the angle xcex8 is 0xc2x0.
The xe2x80x9ccenter portionxe2x80x9d described in Structure (2) means a portion where angle xcex8 on an optical functional surface on the lens surface is 0xc2x0, while, the xe2x80x9cperipheral portionxe2x80x9d means a portion where angle xcex8 on an optical functional surface on the lens surface is not 0xc2x0. With respect to this point, when the peripheral portion is specified in the following Structures to have angle xcex8 of not less than 45xc2x0 or angle xcex8 of not less than 50xc2x0, the xe2x80x9cPeripheral portionxe2x80x9d means a portion of the optical functional surface on the lens surface satisfying the aforementioned condition.
In the invention described in Structure (2), it is possible to prevent a fall of an amount of light passing through the peripheral portion of the lens surface where the angle xcex8 is not less than 45xc2x0. Therefore, it is possible to improve light-converging characteristics more in the optical lens that has the lens surface on which the angle xcex8 is relatively great and has high NA, and thereby to contribute to realization of a large capacity of an optical recording medium.
Structure (3) of the invention is the optical lens according to Structure (1) or Structure (2), wherein, thickness of the antireflection coating is established so that a wavelength wherein reflectance for light entering at angle 0xc2x0 for the antireflection coating on the peripheral portion of the lens surface shows the minimum value is equal to or greater than a wavelength wherein reflectance for light entering at angle 0xc2x0 for the antireflection coating on the center portion of the lens surface shows the minimum value.
xe2x80x9cEqual to or more than a wavelengthxe2x80x9d described in Structure (3) means to be equal to or greater than the wavelength, and xe2x80x9creflectance for light entering at angle 0xc2x0xe2x80x9d shows reflectance in the occasion wherein light is made to enter at angle 0xc2x0 to the antireflection coating for the purpose of measuring reflectance, which also applies to the following Structures.
In the invention according to Structure (3), a wavelength wherein reflectance for light entering at angle 0xc2x0 to the antireflection coating on the peripheral portion of the lens surface shows the minimum value is equal to or greater than a wavelength wherein reflectance for light entering at angle 0xc2x0 to the antireflection coating on the center portion of the lens surface shows the minimum value.
It is therefore possible to control surely so that wavelength-dependency of reflectance on the peripheral portion of the lens surface for light entering obliquely may be shifted less to the short wavelength side, for wavelength-dependency of reflectance on the center portion of the lens surface for light entering vertically. It is therefore possible to prevent surely a fall of an amount of light passing through the peripheral portion of the lens, and to make a spot diameter small to secure an amount of light passing through the lens.
Structure (4) of the invention is the optical lens according to either one of Structure (1)-Structure (3), wherein thickness of the antireflection coating is established so that a wavelength wherein reflectance for light entering the antireflection coating on at least a part of the peripheral portion of the lens surface at angle 0xc2x0 shows the minimum value may be the same as a wavelength wherein reflectance for light entering the antireflection coating on the center portion of the lens surface at angle 0xc2x0 shows the minimum value.
In the invention according to Structure (4), a wavelength wherein reflectance for light entering at angle 0xc2x0 to the antireflection coating on at least a part of the peripheral portion of the lens surface shows the minimum value is the same as a wavelength wherein reflectance for light entering at angle 0xc2x0 to the antireflection coating on the center portion of the lens surface shows the minimum value. In other words, it is prevented that wavelength-dependence of reflectance for light entering a peripheral portion of the lens surface obliquely is shifted greatly toward the short wavelength side, compared with wavelength-dependence of reflectance for light entering a center portion of the lens surface vertically.
It is therefore possible to control reflectance on the peripheral portion of the lens surface for light to be as low as that on the center portion of the lens surface. Thus, an amount of light passing through a peripheral portion of the lens can be made as large as that of light passing through the center portion of the lens, which makes an amount of light passing through the total lens to be increased greatly.
Structure (5) of the invention is the optical lens according to either one of Structures (1)-(4), that is provided on an optical information recording and reproducing apparatus equipped with a laser light source having at least one kind of wavelength in a wavelength range of 630-680 nm, and converges light emitted from the laser light source on an optical recording medium, wherein an antireflection coating is provided on the lens surface on the side where light emitted from the laser light source enters, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 45xc2x0 or more may show the minimum value within a range of 630-800 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side where light emitted from the laser light source enters and by an optical axis.
In the invention according to Structure (5), more light emitted from the laser light source having at least one kind of wavelength in a wavelength range of 630-680 nm can pass through the peripheral portion of the lens, compared with the past, because thickness of the antireflection coating is established as described above.
Structure (6) of the invention is the optical lens according to Structure (5), wherein thickness of the antireflection coating provided on the lens surface on the side where light emitted from the laser light source enters is established so that reflectance for light entering, at an angle of 0xc2x0, the center portion of the lens surface having angle xcex8 of 0xc2x0 may show the minimum value within a wavelength range of 580-740 nm.
Structure (7) of the invention is the optical lens according to Structure (5) or Structure (6), wherein an antireflection coating is provided on the lens surface on the side from which the light emerges to an optical recording medium, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 630-800 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side from which the light emerges and by an optical axis.
In the invention according to each of Structure (6) and Structure (7), it is possible to secure a relatively large amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 630-680 nm and passes through the center portion of the lens because thickness of each of the antireflection coatings is established as stated above.
Structure (8) of the invention is the optical lens according to either one of Structure (5)-Structure (7), that is provided on an optical information recording and reproducing apparatus equipped with a laser light source having at least one kind of wavelength in a wavelength range of 630-650 nm, and converges light emitted from the laser light source on an optical recording medium, wherein an antireflection coating is provided on the lens surface on the side where light emitted from the laser light source enters, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 45xc2x0 or more may show the minimum value within a range of 660-770 nm, and reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 600-700 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side where light emitted from the laser light source enters and by an optical axis, and an antireflection coating is provided on the lens surface on the side from which the light emerges, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 640-740 nm.
In the invention according to Structure (8), it is possible to make an amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 630-650 nm and passes through the peripheral portion of the lens to be more, and to secure more amount of light being emitted from the laser light source and passing through the center portion of the lens, because thickness of each of the antireflection coatings is established as described above.
Structure (9) of the invention is the optical lens according to Structure (8), wherein an antireflection coating is provided on the lens surface on the side where the light emitted from the laser light source enters, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 50xc2x0 or more may show the minimum value within a range of 670-770 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side where the light emitted from the laser light source enters and by an optical axis.
In the invention according to Structure (9), it is possible to make an amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 630-650 nm and passes through the peripheral portion of the lens surface where angle xcex8 is 50xc2x0 or more to be more, because thickness of each of the antireflection coatings is established as described above. Therefore, it is possible to improve light-converging characteristics more in the optical lens having high NA in which the angle xcex8 is extremely great, and thereby to contribute to realization of a large capacity of an optical recording medium.
Structure (10) of the invention is the optical lens according to either one of Structure (5)-Structure (7), that is provided on an optical information recording and reproducing apparatus equipped with a laser light source having at least one kind of wavelength in a wavelength range of 650-670 nm, and converges light emitted from the laser light source on an optical recording medium, wherein an antireflection coating is provided on the lens surface on the side where light emitted from the laser light source enters, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 45xc2x0 or more may show the minimum value within a range of 660-800 nm, and reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 610-740 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side where light emitted from the laser light source enters and by an optical axis, and an antireflection coating is provided on the lens surface on the side from which the light emerges, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 660-740 nm.
In the invention according to Structure (10), it is possible to make an amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 650-670 nm and passes through the peripheral portion of the lens to be more, and to secure more amount of light being emitted from the laser light source and passing through the center portion of the lens, because thickness of each of the antireflection coatings is established as described above.
Structure (11) of the invention is the optical lens according to Structure (10), wherein an antireflection coating is provided on the lens surface on the side where the light emitted from the laser light source enters, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 50xc2x0 or more may show the minimum value within a range of 700-800 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side where the light emitted from the laser light source enters and by an optical axis.
In the invention according to Structure (11), it is possible to make an amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 650-670 nm and passes through the peripheral portion of the lens surface where angle xcex8 is 50xc2x0 or more to be more, because thickness of each of the antireflection coatings is established as described above. Therefore, it is possible to improve light-converging characteristics more in the optical lens having high NA in which the angle xcex8 is extremely great, and thereby to contribute to realization of a large capacity of an optical recording medium.
Structure (12) of the invention is the optical lens according to either one of Structure (1)-Structure (4), that is provided on an optical information recording and reproducing apparatus equipped with a laser light source having at least one kind of wavelength in a wavelength range of 400-450 nm, and converges light emitted from the laser light source on an optical recording medium, wherein an antireflection coating is provided on the lens surface on the side where light emitted from the laser light source enters, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 45xc2x0 or more may show the minimum value within a range of 420-520 nm.
In the invention according to Structure (12), it is possible to make an amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 400-450 nm and passes through the peripheral portion of the lens to be more, compared with the past, because thickness of the antireflection coating is established as described above.
Structure (13) of the invention is the optical lens according to Structure (12), wherein thickness of the antireflection coating provided on the lens surface on the side where light emitted from the laser light source enters is established so that reflectance for light entering, at an angle of 0xc2x0, the center portion of the lens surface having angle xcex8 of 0xc2x0 may show the minimum value within a wavelength range of 380-490 nm.
Structure (14) of the invention is the optical lens according to Structure (12) or Structure (13), wherein an antireflection coating is provided on the lens surface on the side from which the light emerges to an optical recording medium, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 400-490 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side from which the light emerges and by an optical axis.
In the invention according to Structure (13) and Structure (14), it is possible to secure a relatively large amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 400-450 nm and passes through the center portion of the lens, because thickness of each of the antireflection coatings is established as stated above.
Structure (15) of the invention is the optical lens according to either one of Structure (12)-Structure (14), that is provided on an optical information recording and reproducing apparatus equipped with a laser light source having at least one kind of wavelength in a wavelength range of 400-420 nm, and converges light emitted from the laser light source on an optical recording medium, wherein with respect to an antireflection coating provided on the lens surface on the side where light emitted from the laser light source enters, thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 45xc2x0 or more may show the minimum value within a range of 420-490 nm, and reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 380-440 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side where light emitted from the laser light source enters and by an optical axis, and with respect to an antireflection coating provided on the lens surface on the side from which the light emerges, thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the center portion of the lens surface where angle xcex8 is 0xc2x0 may show the minimum value within a range of 400-490 nm.
In the invention according to Structure (15), it is possible to make an amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 400-420 nm and passes through the peripheral portion of the lens to be more, and to secure more amount of light being emitted from the laser light source and passing through the center portion of the lens, because thickness of each of the antireflection coatings is established as described above.
Structure (16) of the invention is the optical lens according to Structure (15), wherein an antireflection coating is provided on the lens surface on the side where the light emitted from the laser light source enters, and thickness of the antireflection coating is established so that reflectance for light entering, at angle 0xc2x0, the peripheral portion of the lens surface where angle xcex8 is 50xc2x0 or more may show the minimum value within a range of 430-490 nm, when xcex8 represents an angle formed by a normal line at a certain position on the lens surface on the side where the light emitted from the laser light source enters and by an optical axis.
In the invention according to Structure (16), it is possible to make an amount of light that is emitted from the laser light source having at least one kind of wavelength in a wavelength range of 400-420 nm and passes through the peripheral portion of the lens surface where angle xcex8 is 50xc2x0 or more to be more, because thickness of each of the antireflection coatings is established as described above. Therefore, it is possible to improve light-converging characteristics more in the optical lens having high NA in which the angle xcex8 is extremely great, and thereby to contribute to realization of a large capacity of an optical recording medium.
Structure (17) of the invention is the optical lens according to either one of Structure (1)-Structure (16), wherein thickness of the antireflection coating on the peripheral portion of the lens surface is (1-1.5) times that of the antireflection coating on the center portion of the lens surface.
In the invention according to Structure (17), it is possible to control a change in a lens form caused by an antireflection coating to be relatively less, because thickness of the antireflection coating on the peripheral portion of the lens surface is (1-1.5) times that of the antireflection coating on the center portion of the lens surface.
Incidentally, to keep a change in a lens form caused by an antireflection coating to be more less, it is more preferable that thickness of the antireflection coating on the peripheral portion of the lens surface is (1-1.2) times that of the antireflection coating on the center portion of the lens surface.
Structure (18) of the invention is an optical information recording and reproducing apparatus that is provided with a laser light source and the optical lens according to either one of Structure (1)-Structure (17), and is capable of conducting at least one of recording information on an optical recording medium and reproducing information recorded on an optical recording medium, by converging light emitted from the laser light source on an optical recording medium with the optical lens.
In the invention according to Structure (18), a light spot diameter is made to be smaller, compared with the past, and more amount of light passing through the lens can be secured, because the light emitted from the laser light source is converged on an optical recording medium by the optical lens.
It is therefore possible to record information on an optical recording medium on a higher density basis and to reproduce information from the optical recording medium on which information is recorded on a high density basis, compared with the past, thus, a large capacity of the optical recording medium can be realized.